This invention relates to an optical information recording apparatus, such as an apparatus for an optical disc file, etc., recording information by irradiating a moving recording medium with focused laser light.
In an optical information recording apparatus, such as an optical disc device, etc., a laser light beam is used as recording means. This laser light beam is intensity-modulated, depending on data to be recorded and focused in an extremely small spot by means of an optical lens so that binary information is recorded by the fact that the heat energy thereof alters portions of recording medium irradiated with light so as to form recorded marks. FIG. 1 indicates the relation between data to be recorded (recording pulses) 1 and ideal recorded marks 2 formed on the recording medium, in which information is recorded as an example in the form of the mark length. In FIG. 1, since information contained in the data to be recorded (recording pulses) 1 corresponds to the boundary between the presence and the absence of the marks 2, it is important how precisely in the position the extremities of the marks are formed. By the prior art recording method using rectangular laser light pulses the marks have the shape of a tear drop 50, the front end portion of which is narrower than the rear end thereof, because of influences of the thermal conductivity of the recording medium, as indicated in FIG. 2.
As a method for correcting these phenomena there is known a method, by which information is recorded with laser light pulses, whose intensity is so regulated that it is higher at the front end than at the rear end thereof, as disclosed in Nos. JP-A-60-25032, JP-A-60-87440, JP-A-60-247827, JP-A-58-182144, and U.S. Pat. No. 4,646,103 (refer to the waveform of the laser light intensity 51 in FIG. 3 and the waveform of the laser light intensity 61 in FIG. 4).
However, when the recording density is increased and the interval between laser light pulses is shortened, the temperature of the recording medium is excessively increased at the front end portion of the laser light pulses because of the thermal conductivity from the directly preceding recorded mark, which gives rise to displacement 53 or 63 in the position of the leading edge of recorded marks, as indicated by the shapes of mark 52 and 62 in FIGS. 3 and 4, respectively. The amount of this displacement 53, 63 varies, depending on the interval between laser light pulses, the distance between two adjacent marks, etc., which gives rise to a drawback that jitter is produced at the recording/reproduction.